A communication system includes DownLink (DL) transmissions that convey signals from transmission points such as Base Stations (BSs) or NodeBs to User Equipment (UEs) and UpLink (UL) transmissions that convey signals from UEs to reception points such as NodeBs. A UE, also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be a cellular phone, a personal computer device, etc. A NodeB, which is generally a fixed station, may also be referred to as an access point or other equivalent terminology.
DL signals consist of data signals conveying information content, control signals conveying DL Control Information (DCI), and Reference Signals (RS), which are also known as pilot signals. A NodeB transmits data information or DCI to UEs through respective Physical DL Shared CHannels (PDSCHs) or Physical DL Control CHannels (PDCCHs). A NodeB may transmit multiple RS types including a UE-Common RS (CRS) that is transmitted over substantially an entire DL BandWidth (BW) and a DeModulation RS (DMRS) that is transmitted in a same BW as an associated PDSCH or PDCCH. UL signals also consist of data signals conveying information content, control signals conveying UL Control Information (UCI), and RS. A UE transmits data information or UCI to a NodeB through a respective Physical UL Shared CHannel (PUSCH) or a Physical UL Control CHannel (PUCCH). If a UE simultaneously transmits data information and UCI, it may multiplex both in a PUSCH.
A PDSCH transmission to a UE or a PUSCH transmission from a UE may be in response to dynamic scheduling or to Semi-Persistent Scheduling (SPS). With dynamic scheduling, a NodeB conveys to a UE a DCI format through a respective PDCCH. The contents of a DCI format, and consequently its size, depend on a Transmission Mode (TM) a UE is configured for a respective PDSCH reception or PUSCH transmission. With SPS, a PDSCH or a PUSCH transmission is configured to a UE by a NodeB through higher layer signaling, such as Radio Resource Control (RRC) signaling, and occurs at predetermined Transmission Time Intervals (TTIs) and with predetermined parameters as informed by the higher layer signaling. UCI includes acknowledgment information associated with a use of Hybrid Automatic Repeat reQuest (HARQ) and is in response to correct or incorrect, respectively, receptions of data Transport Blocks (TBs) in a PDSCH or in response to an SPS release.
Accordingly, there is a need for improved techniques for transmission and reception of HARQ acknowledgment (ACK) signals referred to as HARQ-ACK signals.